The oxygenators developed to date are broadly classified into bubble type oxygenators and membrane type oxygenators. The membrane type oxygenators fall under the laminate type, the coil type, and the hollow fiber type. The membrane type oxygenators excel over the bubble type oxygenators since the membrane type oxygenators cause only slight blood injuries such as hemolysis, protein denaturation and blood coagulation as compared with the bubble type oxygenators, and have been gaining in popularity in recent years. In the membrane type oxygenators, those which use porous gas-exchange membranes have growing utility because they possess a high gas exchange capacity. Membrane type oxygenators using such a porous gas-exchange membrane are disclosed in Japanese Patent Laid-Opens SHO 54(1979)-160,098 and SHO 57(1982)-136,456, for example.
When these conventional membrane type oxygenators are used for extra-corporeal blood circulation as in the cardiotomy and the extra-corporeal membrane oxygenation (ECMO), for example, the so-called general heparinization or the administration of heparin is used to prevent blood coagulation within the oxygenator and the path for extra-corporeal circulation. The general heparinization, however, has a disadvantage since it disrupts the normal intra-corporeal blood coagulating ability, and hemorrhaging from the cut and the operated part cannot be prevented. As a means of decreasing the amount of heparin to be injected, there has been devised a method of continuously injecting a minute amount of heparin into the path for extra-corporeal circulation. This method, however, includes a possibility that the hemorrhage will not be curbed as effectively as expected because of the difficulty experienced in the control of the amount of heparin to be injected or, conversely, a possibility that the injection will induce blood coagulation on the surface of the gas-exchange membrane in the oxygenator and occlusion of the hollow-fiber membrane used as the gas-exchange membrane.
This invention, therefore, is aimed at providing a membrane type oxygenator which effects continuous release of a blood anticoagulant to preclude blood coagulation on the surface of the gas-exchange membrane and occlusion of the gas-exchange membrane particularly in the interior of the membrane type oxygenator even when the amount of heparin to be administered is small.